There is a worldwide interest in capturing and sequestering or reusing carbon dioxide (CO2) emissions to stabilize the climate. Aqueous amine processes, widely used throughout the natural gas industry to reduce CO2 from gas streams via chemical reaction, represent the benchmark by which CO2 capture technologies are evaluated (NETL, Carbon Sequestration Technology Roadmap and Program Plan (2007); Rochelle, G. T., “Amine Scrubbing for CO2 Capture,” Science, 325:1652-1654 (2009)). While effective at reducing CO2 from gas streams, amine processes are highly energy intensive, with much of the energy penalty attributed to boiling water during amine regeneration. Thus, aqueous amine processes will inherently suffer from large energy penalties. However, new solvents with little or no volatility can provide the desired energy efficiency.
Amino acid salts have been proposed as a type of “advanced” amine for CO2 capture. Amino acid salts are neutralized forms (i.e., metal salts) of naturally occurring amido acids such as glycine. Aqueous solutions of amino acid salts, such as sodium glycinate, represent alternatives to conventional amine-based solvents for post-combustion CO2 capture applications.
Relative to amines, amino acid salts can feature benefits of reduced amine volatility (due to the ionic nature of the compound), greater stability in the presence of oxidizers found in flue gas (e.g., O2, SO2, and NOR), and a more rapid reaction rate with CO2, likely due to the enhanced basicity of solvent due to the presence of a basic carboxylate paired with an amine. Amino acid salts are thus a promising approach. However, because the salts are based on a narrow range of naturally occurring compounds, amino acid salts are limited in the tunability of their structures to drive improved CO2 capture applications. Thus, alternative structures with increased tunability are needed.